We bought the Block Rocker Blue Tooth System at Costco for our gym and love it. It was recommended by a LaCrosse coach who uses it outside. I am sure its available elsewhere but here's the link for Costco: http://www.costco.com/Block-Rocker-Bluetooth-Speaker-System.product.1000...
I see the SHURE brand at a lot of facilities.
If you are looking for a portable system, I use a Hisonic HS120 system for my outdoor classes and pool classes. I occasionally use it inside as well if the sound system is down. Light weight compact and decent sound. It has bluetooth as well. Only about $100 on Amazon.